Effect of the Mid-frequency Magnetron Sputtering Current on the Tribological Properties of Si-DLC Films

LIU Longlong; WANG Shaohui; JIANG Chengyan; CHAI Liqiang; WANG Peng; LI Yong; HU Yong

doi:10.16490/j.cnki.issn.1001-3660.2026.05.004

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Surface Technology ›› 2026, Vol. 55 ›› Issue (5) : 54-67. DOI: 10.16490/j.cnki.issn.1001-3660.2026.05.004

Friction, Wear and Lubrication

Effect of the Mid-frequency Magnetron Sputtering Current on the Tribological Properties of Si-DLC Films

LIU Longlong¹, WANG Shaohui^1,2, JIANG Chengyan³, CHAI Liqiang^2,*, WANG Peng², LI Yong⁴, HU Yong^1,*

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Abstract

Diamond-like carbon (DLC) films are widely recognized for their exceptional hardness, low friction and wear resistance, but their performance at elevated temperatures and under high stress remains limited due to graphitization and internal stress accumulation. To address these challenges, the work aims to systematically investigate the role of silicon (Si) doping and sputtering current modulation in enhancing the tribological properties of Si-DLC films under both ambient and high-temperature conditions. The originality of this work lies in the precise control of mid-frequency magnetron sputtering parameters to tailor the sp³—C hybridization content, Si distribution, and stress-relief mechanisms, thereby optimizing the mechanical and tribological properties of the films.
Si-DLC films were deposited on W18Cr4V steel substrates and silicon wafers through mid-frequency magnetron sputtering with varying currents (1-3 A). A Cr layer was first deposited by DC magnetron sputtering (20 min) to enhance the adhesion between the film and the substrate. Subsequently, Si-DLC films were deposited through mid-frequency pulsed magnetron sputtering (MFMS) of a silicon target in an Ar/CH₄ mixed atmosphere. The microstructure and composition of the films were characterized through field-emission scanning electron microscopy (SEM), atomic force microscopy (AFM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Surface roughness and cross-sectional morphology were analyzed to evaluate film uniformity and defect density. Mechanical properties, including hardness and elastic modulus, were measured via nanoindentation. Tribological properties were assessed with a ball-on-disc tribometer test (GCr15 steel ball counterpart, 5 N load, 0.1 m/s sliding speed) and an HT-1000 high-temperature friction tester (100-300 ℃). Wear tracks and counterpart ball scars were examined via optical microscopy to determine cross-sectional wear profiles. Raman spectroscopy and energy-dispersive spectroscopy (EDS) were conducted on the wear tracks (center/edge) and ball scars (center/edge) to analyze phase transformations and tribochemical reactions.
The Si-DLC films exhibited dense, uniform surfaces without cracks or voids. As the sputtering current increased, the sp³—C hybridization content rose from 10.12at.% (1 A) to 21.00at.% (3 A), accompanied by enhanced hardness (10.98 GPa to 13.10 GPa) and elastic modulus (87.90 GPa to 104.00 GPa). Moderate Si doping effectively relieved internal stress. The film deposited at 1.5 A demonstrated superior room-temperature tribological properties, with an average friction coefficient below 0.04 and a wear rate of 2.78×10^-7 mm³/(N·m). At 300 ℃, the low-current (1 A) film maintained excellent friction stability (average coefficient: 0.1, wear rate: 4.16×10^-7 mm³/(N·m)), whereas the high-current (2 A) film suffered severe wear and a sharp rise in friction. Optimizing the mid-frequency sputtering current significantly enhances the tribological properties of Si-DLC films at both room and elevated temperatures. Higher Si content promotes an abrasive wear mechanism. This study elucidates the mechanism by which sputtering current modulates the Si content and sp³—C ratio, thereby affecting the mechanical properties and tribological behavior of Si-DLC films. This work not only clarifies the interplay between Si doping and sp³—C content but also establishes a novel strategy for enhancing DLC durability in extreme environments, marking a advanced step forward in tribological coating technology. The findings provide critical theoretical insights and technical guidance for developing high-performance Si-DLC films tailored for elevated-temperature applications. The results hold significant implications for expanding the use of DLC films in high-temperature friction systems, such as aerospace components and automotive engines.

Key words

Si-doped DLC films / magnetron sputtering / current / mechanical properties / tribological properties / wear mechanism

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LIU Longlong, WANG Shaohui, JIANG Chengyan, CHAI Liqiang, WANG Peng, LI Yong, HU Yong. Effect of the Mid-frequency Magnetron Sputtering Current on the Tribological Properties of Si-DLC Films[J]. Surface Technology. 2026, 55(5): 54-67

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Funding

The National Key Research and Development Program of China (2022YFB3809000); the Key Research and Development Program of Gansu Province (22YF7GA156); the Gansu Higher Education Innovation Project (2025A-232); the Gansu Science and Technology Major Projects (23ZDGA01, 22ZD6GA008); the Hongliu First-Class Discipline Support Program of Lanzhou University of Technology (CGZH001)